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ATEL # 1804; T. Belloni (INAF- Brera Observatory), J. Homan (MIT), K. Yamaoka (Aoyama Gakuin Univ.), J. Swank (NASA/GSFC)
on 23 Oct 2008; 12:38 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Tomaso Belloni (email@example.com)
Subjects: X-ray, Binaries, Black Holes, Transients
Referred to by ATEL #: 1808
An RXTE observation of H 1743-322 made on 2008 October 23 03:18-04:39 UT indicates that the source has undergone a state transition from the Low-Hard State (LHS) to the Hard-Intermediate State (HIMS) (see also ATel #1780, #1779, #1766, #1745, #1739). The power density spectrum shows band limited noise with a characteristic frequency of around 5 Hz and a prominent quasi-periodic oscillation with centroid frequency of 5.6 Hz and a coherence factor Q ~ 10. The 0.1-20.0 Hz fractional rms is 15%. These values are all indicative of a HIMS. We note that during the previous observation (on 2008 Oct. 19) the QPO was at 1 Hz. The PCA energy spectrum in the 3-25 keV range can be fitted with a power law (photon index 2.02 +/- 0.02 and flux 2.3e-9 erg/cm2/s) plus a disk-blackbody (inner disk temperature 0.78 +/- 0.02 keV, inner radius 19 +/- 1 km at 10 kpc distance and a flux of 4.9e-10 erg/cm2/s) and some evidence of a broad Gaussian emission line at 6.4 keV. The absorption was fixed at 2.2e22 cm-2. Also these spectral parameters are typical of a HIMS. The fast evolution of the timing and spectral parameters indicate that H 1743-322 is most likely approaching a transition to the Soft-Intermediate State, with appearance of a type-B QPO and a considerable softening of the energy spectrum. Further multi-wavelength observations are strongly encouraged, in particular in the radio band, as the HIMS-SIMS transition has been positively associated to the ejection of relativistic jets.